The URL:MAL detections are usually from the Network Shield and there are no user settings in that where you can exclude a site from further alerts. Essentially it has to be investigated, confirmed clean and then removed from the malicious sites list. So each instance has to be investigated (why I asked about a specific URL) and reported.
This can be done using the on-line contact form,
http://www.avast.com/contact-form.php?loadStyles for: * Sales inquiries; Technical issues; Website issues; Report false virus alert in file;
Report false virus alert on website; Undetected Malware; Press (Media), issues.
- If you are reporting an FP, then you get another input field open, enter the web URL for the site you wish to submit for review (Network Shield), etc. A link to this topic also wouldn't hurt.
Avast won't take a URL as safe as such, the fact that it worked fine in the past is no guarantee it will be safe in the future. I believe that is why there is no user exclusion for the network shield. We find that following the above path of reporting in the forums where users can check it out and confirm, before reporting and giving a forum topic (which contains more information than the report can) in the report generally has a quicker positive response.
I don't know what instructions you found, but avast would apply equally to all browsers that are supported not just IE.